Using BAPI_PRICES_CONDITIONS for modification

To update coditions, I use BAPI_PRICES_CONDITIONS (update table A004 and KONP)

tn_bapicondct-operation = '023'.

tn_bapicondct-table_no = '004'.

tn_bapicondct-cond_no = '0000016926'.

tn_bapicondct-cond_usage = 'A'.

tn_bapicondct-applicatio = 'V'.

tn_bapicondct-cond_type = 'PV00'.

tn_bapicondct-varkey = 'OC0102000000000002146041'.

tn_bapicondct-valid_to = '20080131'.

tn_bapicondct-valid_from = '20050517'.

APPEND tn_bapicondct.

tn_bapicondhd-operation = '023'.

tn_bapicondhd-table_no = '004'.

tn_bapicondhd-cond_no = '0000016926'.

tn_bapicondhd-created_by = sy-uname.

tn_bapicondhd-creat_date = sy-datum.

tn_bapicondhd-cond_usage = 'A'.

tn_bapicondhd-applicatio = 'V'.

tn_bapicondhd-cond_type = 'PV00'.

tn_bapicondhd-varkey = 'OC0102000000000002146041'.

tn_bapicondhd-valid_to = '20080131'.

tn_bapicondhd-valid_from = '20050517'.

APPEND tn_bapicondhd.

tn_bapicondit-operation = '023'.

tn_bapicondit-cond_no = '0000016926'.

tn_bapicondit-cond_count = '01'.

tn_bapicondit-applicatio = 'V'.

tn_bapicondit-cond_type = 'PV00'.

tn_bapicondit-scaletype = 'A'.

tn_bapicondit-scalebasin = 'C'.

tn_bapicondit-scale_qty = '1'.

tn_bapicondit-cond_p_unt = '1'.

tn_bapicondit-cond_unit = 'UVC'.

tn_bapicondit-calctypcon = 'C'.

tn_bapicondit-cond_value = '2.09'.

tn_bapicondit-condcurr = 'EUR'.

APPEND tn_bapicondit.

I want to modified an existing condition number to update DATBI and Condition value (KONP-KBETR). But the only update, after launching, is the condition value, the date (valid_to) is not updated. Why ?